The Physics of a Spinning Ring

The above is a link to the video. Sorry, I couldn’t embed it because for some reason, the user disabled embedding. Oh well. Here is a picture of a spinning ring instead.

If you don’t want to watch the clip, let me summarize.

Conan likes to spin his wedding ring on the table.

His best spin keeps the ring spinning for 41 seconds.

In an effort to beat that time, he brings in a physicist.

So, why is this clip so awesome? Here are some thoughts.

Every Physicist Likes Problems

I think the physicist here (Peter Fisher) did a great job. Clearly, he is interested in the problem and he handles himself well. What is cool is that this may seem like a dumb thing to waste his time on, but you never know. A common idea about science is that it is done just to solve big problems. In fact, science isn’t really about problems at all. Science is about observations and making models. If these models turn out to be useful, that is just extra awesome. So, we study spinning rings because we want to model it.

Really, this is exactly the kind of problem that would have made an excellent blog post.

First try not working is important

The attempt at modeling a spinning ring was to assume that the air resistance was the primary cause. After a calculation, Peter thinks that would be an insignificant effect. So, they try it anyway to make sure. Now, if you watch the video, it is probably the case where they didn’t really try this. Mostly because of time. The vacuum chamber they made did not have enough time to get most of the air out to produce an effect. Also, you know how these shows are – they have to move fast.

But this does show the importance of something not working.

Collecting Data with Uncertainty

After considering the importance of friction, Peter tries spinning his own ring at home – both with and without vaseline on the surface. Here is a picture of his data:

I assume this is a histogram of the spin times for the ring. He reports a spin time of 30 +/- 10 seconds on the dry table and 40+/-10 seconds with vaseline. Is that a significant difference? Well, it depends on your statistical test. It is plausible that the times are different. But the point is that he collected multiple runs of data.

Approaching the problem in terms of energy

One last thing. Why does the ring slow down? Well, some energy is transferred. Two possible interactions are the air and the surface. When they put lubricant on the surface, they noticed the spinning ring made less noise. That is a good indication that less energy is being “lost” in that interaction.